Air pollution is a serious health issue throughout the world. More than 100 million people in Latin America reside in areas where air pollution exceeds limits set by the World Health Organization. Air pollution in Mexico City and Sao Paulo has been linked to deaths in adults and children, respiratory problems in children (such as asthma), emergency room visits, and other problems (Bell, 2006). Sixteen of the world's most polluted cities are in China. One third of the country suffers from acid rain, the area around Bejing suffers the worst levels of nitrogen dioxide in the world, and China is second to the U.S. as a producer of greenhouse gases. More than 100 million Chinese reside in areas in which the air pollution can reach levels considered to be very dangerous and air pollution is implicated in more than 400,000 premature deaths per year. There are days in which a quarter of the particulate pollution of Los Angeles originated in China (Watts, 2005). In Europe, air pollution causes twice as many premature deaths as do car accidents (Blatt, 2005).
Air pollution is implicated in sixty thousand deaths per year in the United States. Six percent of Americans have asthma. In the United States, hospital admissions for respiratory problems such as asthma increased during periods of high levels of ozone and sulfur dioxide pollution (Wilson, 2005). Diabetics with a history of heart disease are at a special risk for adverse health effects caused by air pollution (Goldberg, 2006). Children and the elderly are also at high risk for the effects of air pollution. In the U.S. and other industrialized countries, asthma incidence is rising. Between 1979-1991, asthma rates rose 56% for Americans under 18 and children under 4 were the fastest growing group entering the hospital for asthma attacks.
Air pollutants are detoxified in humans by a number of enzymes, including glutathione-S-transferases (GSTs). Deletions of GST genes are relatively common in humans (half of Caucasians suffer a deletion of GSTM1 and 15-20% lack GSTT1). The genetics of GST deletions seem to interact with environmental factors (such as exposure to cigarette smoke) to make the development of childhood asthma more likely (Kabesch, 2006).

--after Kemp, 2004


Is this rain acidic?


Sulfur and nitrogen oxides are respiratory irritants that affect breathing, lower resistance to respiratory infections, and aggravate asthma and emphysema. Nitrogen oxides (nitric oxide NO and nitrogen dioxide N2O form in automobile engines which are not only irritants themselves but react with other molecules to form the components of photochemical smog. Sulfur is a component of coal which produces sulfur dioxide when burned.
The levels of sulfur and nitrogen oxides can reach critical levels in the air. A number of northern Chinese cities have 3-8x the World Health Organization limits for sulfur dioxide. The West German Ruhr region had sulfurous smoke in 1/85 and 2/87 that caused schools to close. The use of private cars was prohibited, there were advisories to stay indoors (especially the young & old), and industry & power stations were told to reduce emissions 30% or shut down. During the Czech winter 1989-90, there were 7 episodes in which bronchitis & lung infections of newborns increased 50% (American Chemical Society, 1994).
During the period of 1980-2000, sulfur emissions decreased 37% in the U.S. and 56% in Europe but increased 250% in Asia. The World Bank estimates that China loses $5 billion per year due to the effects of acid rain (Speth, 2004).

Sulfur and nitrogen oxides in themselves are not only dangerous, they can produce acid when mixed with water.
4 NO2 + 2 H2O + O2------------' 4 HNO3 (nitric acid)
2 SO2 + O2 ------------------------' 2 SO3
SO3 + H2O---------------'H2SO4 (sulfuric acid)
The acids produced in the atmosphere lead to acid rain, acid snow, and acid fog. The most tragic incident related to this was a deadly fog over London in 1952 which caused 4000 deaths. A similar fog in Donora, Pa. in 1948 caused 20 deaths. Thanks to better pollution standards, deadly fogs are a thing of the past (American Chemical Society, 1994).

Water molecules (H2O) can dissociate into H+ and OH- ions. Pure water is neither acidic nor basic since there is a balance between these two ion concentrations. Other compounds can also produce these ions-acids produce H+ ions (as in hydrochloric acid HCl below) and many bases produce OH- ions (such as sodium hydroxide NaOH below).

dissociation of water, acid, base

How many H+ ions exist can make the difference between life and death. The pH scale is a scale to measure the concentration of H+; water is neutral (since [H+] = [OH-]) and represents a pH of 7. Acids have a higher concentration of H+ and have pH values of 0-6.9. The lower the pH, the stronger the acid. Bases remove H+ from solution and have pH values of 7.1-14. The higher the pH the stronger the base.

pH scale

While normal rainwater has a pH between 5.3-6.0 (this is slightly acidic due to carbon dioxide dissolving in water to form carbonic acid), the average rainfall of much of the northeast NE U.S. is pH 4.5. Some fogs of Southern California have registered pH 2.5 and 1.5. Scotland had a rainstorm of pH 2.4; central China has had rainstorms and streams of pH 2.

National Academy of Sciences estimates that acid rain causes $6 billion a year in damages in the U.S.
--It erodes limestone and marble, rusts iron, and causes the deterioration of paint.
--It aggravates respiratory illnesses such as asthma and emphysema.
--It dissolves heavy metals in underwater sediments and dissolves lead from water pipes into drinking water. At pH 6.3 water dissolves .03 µg Pb (lead)/g water; at pH 4.4 it dissolves .8 µg; at pH 2.4 it dissolves 8.6 µg.
--Lower pH water kills fish. Healthy lakes have pHs of about 6.5. At a pH 5.5 many fish disappear and at pH 5.0 most aquatic life disappears. A lake with a pH of 4.0 is essentially dead. Most of the lakes of Scandinavia are dead due to acid rain. In the Northeastern United States, the damage of acid rain on the fishing industry was estimated to fall between $5.3 and 27.5 milllion. Acid rain in Norway may cost the fishing industry 1 million dollars (Mentz, 2004). Not only is the annual pH of rainwater important, but so is the occurrence of episodic acid rain events. Such events have been shown to effect the wetlands of the Northeastern U.S (Lawrence, 2002).
--Acid leaches nutrients from soil and changes the populations of soil organisms. This slows rates of organic decay and changes plant species that can survive in the soil. There has been massive tree deterioration and death in Germany & Eastern Europe; many U.S. forests also suffer. As soil pH drops, plants suffer periodic aluminum toxicity. If the soil pH drops to 3.0-4.2 loss of biomass and the loss of certain species. In soils under pH 3.5, only plants with root systems restricted to the top soil layer can survive. In the Northeastern U.S. and Canada, there is evidence of acid rain damaging forests, such as those composed of sugar maple and higher altitude red spruce (Mentz, 2004).
-- Acid rain can negatively effect the distribution of wildlife, such as the wood thrush (Hames, 2002).

In 1980 several northeastern states and Canada sued the EPA to take stronger measures against acid rain (Mentz, 2004). In 1980, the Acid Precipitation Act led to the formation of the National Acid Precipitation Assessment Program (NAPAP). Its 1998 report warned of adverse effects due to prolonged acid rain over multiple decades (Mentz, 2004). Under the Clean Air Act of 1990, sulfur dioxide levels were to be capped at 8.9 million tons by the year 2000. The Clean Skies Initiative would cap sulfur dioxide at 4.5 million tons by 2010 and nitrogen oxide production to 2.1 million tons by 2008 (Mentz, 2004).
Acid rain remains a problem in the Northeastern United States, in Europe, and in Southeast Asia. Chinese coal consumption is the second greatest in the world and Chinese coal possesses high amounts of sulfur. The resulting acid rain affects much of China and even Japan and Korea. Some cities have annual pH levels of 3. The amount of China which was affected by acid rain increased from under 11% in 1985 to about 25% in 1993 (Terada, 2002).

There are other air pollutants which people are exposed to. These pollutants are especially a problem for those who live in cities, whether the city is Asuncion, Paraguay, Rio de Janeiro, or New York City.



New York

While atmospheric ozone is required for life on earth, it is potentially harmful when it is breathed. At low altitudes, it is a pollutant. Even low concentrations of ozone can decrease lung function in healthy people and it worsens asthma. Maximum hourly concentrations of .05 ppm may cause headaches, concentrations of .15 ppm cause eye irritation, and concentrations of .29 cause coughs and chest discomfort. In L.A. 9/79, there were 10 consecutive days in which ozone concentrations exceded .35 ppm. Hospital admittance of emphysema and asthma patients increased up to 50%. Ozone levels in Mexico City are a serious problem for much of the year. Low altitude ozone also damages plants and is estimated to cause $3 billion in damage in the U.S. Ozone is blamed in part for the dieback of forests in Mexico, Israel, and parts of Europe.

CO (carbon monoxide) causes more deaths in U.S. than any other gas. The hemoglobin in red blood cells binds carbon monoxide 210 times as well as it binds oxygen. When 70-80% of a person's hemoglobin have bound CO, death results. Chronic sublethal exposure to carbon monoxide may lead to brain damage and mental changes. When fossil fuels undergo combustion without sufficient oxygen, carbon monoxide is produced. Several hours in air that is 1 ppm (part per million) carbon monoxide can cause death; the amount produced in heavy traffic can result in headaches, drowsiness, & blurred vision. Industry, cars, fossil fuel burning, and slash and burn agriculture produce 1500 tetragrams of carbon monoxide (1012 grams)/ year.

In 1975, the catalytic converter was added to cars to reduce the amount of carbon monoxide produced by the combustion of gasoline. Although the number of cars in America doubled between 1970 and 1990, carbon monoxide emissions dropped by almost 40% (American Chemical Society, 1994).


Particulates are small pieces of solid materials dispersed into the atmosphere. When Kuwait's oil wells were set afire during the Persian Gulf War, an estimated 4 million barrels of oil (whose sulfur content was 2.5%) burned per day producing 20,000-40,000 tons of sulfur dioxide & 100,000 tons of sooty smoke. The decrease in temperature caused by the soot was estimated to be 4-10oC. Particulate pollution has been a problem in the past. In Europe & North America in the 1930s-40s, many urban areas received less than 50% of their potential winter sunshine. It was not uncommon for Pittsburgh & London to require streetlights during the day. Some particulate pollution raises additional health concerns. Asbestos (from brake linings & insulation), for example, can cause cancer.
Increased levels of particulate air pollution, even when these levels are below the EPA accepted limits, are correlated with an increased number of patients with congestive heart failure admitted to hospitals in the U.S. cities. The elderly, diabetics, and patients with a history of heart disease were more likely to be affected (Wellenius, 2006). The emissions of carbon particulates and sulfur dioxide from coal has increased more than 6 times in South Asia since 1930. These pollutants have resulted in the formation of atmospheric brown clouds which have cooled surface temperatures and reduced rainfall amounts. The frequency of drought and other adverse climate changes in South Asia may increase as these emissions increase (Ramanathan, 2005). Particulate air pollution causes some of its adverse health effects through oxidative damage to DNA (Risom, 2005). Higher levels of particulate air pollution increase the risk of heart attack, ventricular arrhythmias, artery acute vasoconstriction, and the number of hospital emissions for cardiovascular disease (Peters, 2001; Rich, 2005; Brook, 2002).

Because of human activity and air pollution, cities are usually warmer than the surrounding non-urban areas. In the U.S., this urban heat-island effect is usually just over one degree Celsius but it is almost 3 degrees Celsius for New York City. In other parts of the world, this effect causes an increase of more than 3 degrees in Moscow and occasional increases of 6.5 degrees Celsius in China (IPCC, 1990).

For many individuals, the greatest sources of air pollution they experience occur inside the home (Zhao, 2005). Cigarette smoke is a significant source of pollution and there are more than 4,000 chemicals present in cigarette smoke. Other sources of indoor air pollution include the outgassing which occurs from a variety of household items such as carpet to plastics and the allergens which contribute to asthma ranging from pet dander to dust mites.

While there are problems with air pollution today, many problems of the past have already been largely solved. Many areas have much cleaner air than they once did.
Tetraethyl lead, when added to gasoline, prevents premature explosion (knocking) but unfortunately, it is also a neurotoxin, and its release can affect brain development in children. Since 1976, all new cars and trucks in U.S. run on unleaded on unleaded gasoline and annual lead emissions have dropped dramatically. Unfortunately, unleaded gasoline is a little more expensive than leaded gasoline and some developing nations still use leaded gasoline. Leaded gas is still used in Mexico City, where 85% childhood diseases are blamed on air pollution and 32 tons of lead emissions are released per day. Although the U.S. banned tetraethyl lead since 1975, this country still ships it to other countries (American Chemical Society, 1994). Two thirds of the gasoline in China still contains lead (Blatt, 2005). In the photo below of a gas station in Paraguay, note the distinction between the most widely used regular gas which contains lead ("comun") and the super unleaded gas ("super sin plomo").

sign for gas in Paraguay
Clean Air Acts and regulation of pollution have had a major impact on air quality. For example, Pittsburgh's air has greatly improved in the past decades, most Nashville residents don't know city was once called "Smoky Joe", and London's present problems are nothing like the "killer smogs" of the 1950s. Sulfur dioxide, CO, lead, and particulate concentrations have decreased since 1975. Before the British Alkali Act of 1863, bronchitis had been nicknamed the "British Disease".
The Clean Air Act was made law under Nixon and was strengthened under George H. Bush. The EPA concluded that for the time period up to 1990, "an additional 205,000 Americans would have died prematurely and millions more would have suffered illnesses ranging from mild respiratory symptoms to heart disease, chronic bronchitis, asthma attacks, and other severe respiratory problems.". The EPA concluded that the strengthening of the act under George H. Bush could prevent "23,000 premature deaths, and avert over 1.7 million incidents of asthma attacks…67,000 incidents of chronic and acute bronchitis…4.1 million lost work days" per year in the future. (Union of Concerned Scientists, 2004)